Concrete generally exhibits a low tensile strength and low fracture toughness. The ease with which cracks can nucleate and propagate in concrete under tension makes it imperative that concrete not be loaded in tension to the extent possible, and if unavoidable, some form of traditional reinforcement, such as rebar, is ordinarily provided to take the tensile stresses. The latter is generally known as reinforced concrete.
An alternate method of reinforcement is by incorporating short, randomly distributed fibers in concrete such that the reinforcing fibers are distributed throughout the matrix and thus a new composite material, such as fiber reinforced concrete, is obtained. Fiber reinforced concrete has significantly improved energy absorption capability (often called toughness), impact resistance, and fatigue endurance, with greater resistance to cracking. It can also have better durability with an improved appearance.
Concrete has been reinforced with metal, steel and polymer fibers, in some cases strengthening the concrete and even making it blast resistant. Thread-like elements (fibers) of steel wire having uniform corrugations along their entire length have been used for the reinforcement of concrete. Typically steel fibers can be found in different forms: round (cut from wire), flat (sheared from steel sheets), and irregularly shaped from melt. Mechanical deformations such as crimping, adding hooks or paddles at their ends, or roughening their surface sometimes increases the bonding of fiber to matrix.
A significant problem that remains is an efficient and low cost method to manufacture the fibers used in these composites. Current methods are complex and the resultant products relatively costly. Excessive material cost can result in poor reinforcing efficiencies because of the perceived cost to benefit ratio. Accordingly, there is a need for improved fibers and their method of manufacture in order to improve the manufacture of reinforced cement, ceramic, and polymeric based composites. There is also a need for methods of manufacturing fibers having improved geometries at a reduced cost. Fibers with optimized geometry can improve the pull-out load of the fiber, the stress-strain response of the composite under various loadings, and the energy absorbing capacity of the composite. The fibers disclosed here satisfy these needs at a significantly lower cost than is currently available.